# DOF And The 45 mm

Started 4 months ago | Discussion thread
 Like? 1
 Re: DOF And The 45 mm In reply to dgnelson, 4 months ago

dgnelson wrote:

I've been playing with my new 45 mm lens on my omd and realise how much depth of field control there is. I've taken some portraits at f1.8 and can see that they might have been better with a wider dof. I'd be interested in what f stop other people are using for portraits with this lens.

For an 8"x10" print/display size viewed at the standard 25cm viewing-distance (which is what on-line DOF calculators assume), a COC diameter of 15 Microns is assumed for a M43 image-sensor such as the E-M5's (30 Microns for Full Frame divided by the M43 Crop Factor of 2.0).

A smaller COC diamter could be used (as small as 7.5 Microns, which is equal to the height/width of a 2x2 array of the E-M5's approximately 3.75 Micron sized photo-sites). The effect of choosing that (7.5 Micron COC diameter) is to halve the DOF and double the Hyperfocal Distance. This online-DO calculator is the only one that I know which allows the COC diameter to be specified by the user with a sufficiently high degree of numerical precision:

http://www.tawbaware.com/maxlyons/calc.htm

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You can closely approximate the DOF yourself using the formulas below. We presume that you are not shooting close-up/macro, and that the Camera to Subject Distance is a small fraction of the Hyperfocal Distance (less than around 33% for less than 11% error) when using a 45mm FL lens.

Distances in units of Meters:

DOF = (2) x (F) x (C) x ( D / L )^(2)

Distances in units of Feet:

DOF = (0.6096) x (F) x (C) x ( D / L )^(2)

where:

DOF is Depth of Field (in the distance units indicated above);

F is F-Number;

C is Circle of Confusion diameter (in units of Microns);

D is Camera to Subject Distance (in the distance units indicated above);

L is (actual) lens-system Focal Length when focused at infinity (in units of milliMeters).

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In all cases above:

To adjust for a different print/display size (other than 8"x10"), scale the Circle of Confusion Diameter (C) in inverse proportion to the amount of image-enlargement. Note that the minimum Circle of Confusion Diameter (C) is 7.5 Microns for the E-M5's image-sensor. That fact places an upper limit on the print/display size.

To adjust for a viewing-size (other than 25cm), scale the Circle of Confusion Diameter (C) in direct proportion to changes in the viewing-distance.

Edited 4 months ago by Detail Man
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